1. Field of Use
This invention relates generally to tilt indicating devices for mounting on tiltable vehicles or tiltable machine components and to control systems employing such devices.
2. Description of the Prior Art
Tilt indicating devices are used on off-the-road or rough-terrain vehicles to sense when the vehicle, or some movable component thereon, has reached a potentially dangerous tilt angle. Some such devices provide a direct visual indication of tilt so that appropriate corrective action can be taken by the machine driver or operator, while others are connected in control systems which either provide an audio/visual indication of tilt or effect levelling of the tilted vehicles or component. For example, when operating agricultural or construction machinery on a hillside, it is important that the vehicle itself not exceed a cetain tilt angle so as to prevent roll-over. Similarly, when operating vehicles such as cranes or fork-lift trucks which have tiltable components, such as booms or masts, respectively, it is important that the component not exceed a certain tilt angle to prevent vehicle imbalance and possible tip-over.
The prior art discloses many examples of mechanical and electromechanical slope or tilt indicating devices which give a direct read-out or which are employed in control systems which provide a read-out or a control function. For example, U.S. Pat. No. 3,377,714 discloses a device wherein an inverted pendulum type upright float is mounted for pivotal movement about a single axis in a liquid medium and gives a mechanical visual readout. U.S. Pat. No. 3,559,294 discloses a device wherein a float on the surface of a liquid tilts about a single axis and operates a potentiometer to give an electrical readout. U.S. Pat. No. 3,660,840 discloses a device wherein a float on a liquid surface makes electrical contact with four electrical contacts carried at the four corners of a cross-shaped member fixed to the reservoir. Each contact actuates a particular light to thereby indicate one of four possible directions of inclination. U.S. Pat. No. 2,772,411 discloses a device wherein a pendulum in liquid pivots about a single axis and operates a variable resistor to serve as a boom angle indicator for cranes. U.S. Pat. No. 3,945,391 discloses a device wherein a float immersed in liquid rotates about a single axis to operate a valve serving as a boom leveler. U.S. Pat. No. 3,865,265 teaches a device for electrically determining the direction and degree of tilt of the mast of a forklift truck and employs a pendulum immersed in liquid and swingable about a single axis which operates a potentiometer. U.S. Pat. No. 3,846,781 teaches a device wherein there is a pendulum and pointer swingable about a single axis for slope measurement and makes provision for actuating electrical contacts in response to pendulum movement. U.S. Pat. No. 3,805,398 teaches a pivotally mounted freely rotatable magnet which serves as an angle sensor for a drilling tool for earth boring. The magnet position determines energization of sensing coils which effect a readout.